.tab{
	
	width: 635px;
	height: 900px;
	background-color: red;
	
}

.tab2{
	width: auto;
	height: 800px;
	margin: 0 auto;
	overflow-x: hidden; /* 隐藏水平滚动栏 */
	overflow-y: auto;
	background-color: aqua;
}

.tab3{
	width: auto;
	height: 20%;
}